Keishiro Iriya

Development of Low Alkaline Cement Considering Pozzolanic Reaction for Support System in HLW Repository Construction

Cementitious materials have been studied for their applicability as support and lining in the construction of shafts and tunnels of the underground facilities for HLW disposal system. However, in the case of Ordinary Portland Cement (OPC), the buffer materials and the host rock may be altered due to the high alkalinity of groundwater contacting the OPC in the long-term. Low alkaline cements with high content of pozzolanic material were developed in order to reduce such hyper alkaline alteration. This paper shows that the pH of the leaching solution of this cement is about 11, and that it can be applied for full scale lining and for shotcrete.

Experimental study on the water permeability of a reinforced concrete silo for radioactive waste repository

Abstract A low permeable concrete structure is required in a shallow land disposal system in order to isolate radioactive waste from the biosphere. Two model silos (7.25 m dia., 5.25 m height, 1.50 m wall thickness) will be constructed to demonstrate the performance of the concrete structure constructed by the two concepts. One concept is called the improved grouting method . We intend to inject cementitious material to the defective zone such as a crack after its construction by an ordinary construction method. The other concept is called the improved constructing method . We intend to minimize the defective zone, which influences the permeability, during the construction by an improved constructing method. The permeability of the concrete structure as a whole structure will be assessed by two large-scale-model-silos until 1992. The design, objectives, and preliminary results of this experiment are mainly described in this paper.

STUDY ON CREEP BEHAVIOR IN THE UNLOADING PROCESS FOR EARLY AGED CONCRETE

若材齢コンクリートのクリープ挙動に関する研究のうち, 除荷後のクリープ挙動のモデル化について研究した. モデル化の方法として, (1) 除荷後の回復ひずみ関数を構築する方法 (2) クリープ関数を基に重ね合わせ法を適用する方法などがあるが, この両者について実験値と比較して, その適応性を検討した. クリープ試験より, 除荷後の回復ひずみは, 除荷時の応力強度比に依存していることが明らかになったので, 除荷時の応力強度比に着目した回復ひずみ関数を構築した. その関数を段階的に応力が減少する条件下のクリープ試験結果と比較した結果, 良く一致することを確認した. 一方, 重ね合わせ法に関しては, 圧縮応力載荷後の除荷過程を引張応力の増加と考えると実験値とよく一致するが, 圧縮クリープ関数を用いた場合でも適用は可能である.